Controlling the distribution of a load between generator sets (hereinafter “gensets”) is important to avoid overloading and stability problems on the system's gensets. In a paralleled system, load sharing includes the proportional division of the total load of the real power (kW) and reactive power (kVar) between the gensets. Typically, the system includes two separate control systems, namely, an engine speed governor and an automatic voltage regulator (AVR), for controlling the real power and the reactive power, respectively.
Regarding the real power, the engine speed governor of each genset generally determines the proportional sharing of the total real power requirements of the system. The kW load sharing is achieved by increasing or decreasing fuel to the system's engines. The control of the gensets via the engine speed governor involves monitoring and controlling the sharing of the total kW load in proportion to the relative rating of the engines on the system's gensets.
As to the reactive power, an alternator field excitation system of each genset controls the proportional sharing of the total reactive power requirements of the system. The kVar load sharing is achieved by increasing or decreasing the field excitation to the system's alternators. The control of the gensets via the AVR involves monitoring and controlling the sharing of the total kVar load in proportion to the relative rating of the alternators on the system's gensets.
A typical analog load share system use two pairs of bidirectional analog lines connected between gensets. One pair is used for kW sharing and the other for kVar sharing. The lines are used by the gensets to determine how much load each genset should take. They generally operate by each genset applying a voltage to the lines that is proportional to the power on that set. The result of the voltages applied by each genset to the load share lines is a voltage that is proportional the total system load divided by the total number of gensets connected together. By reading this value on the load share lines each genset knows what proportion of the load it should take. Each genset compares this value to the gensets actual load and creates an offset adjustment which is applied to the AVR (to control kVars) or governor (to control kW's) to raise or lower the genset load to match the load measured on the load share lines.